Relaying system



Oct. 19, 1954 R. 1. WARD RELAYING SYSTEM 6 Sheets-Sheet l Filed April 25, 1952 I N VEN TOR.

Ward,

Kum. mw. m wb. QN `Q/ fm,

Oct. 19,` 1954 R. l. WARD RELAYING SYSTEM Filed April 26, 1952 6 Sheets-Sheet 2 fpm Oct. 19, 1954 R. WARD 2,692,352

RELAYING SYSTEM Filed April 26, 1952 6 Sheets-Sheet 3 67, INVENToR.

Oct. 19, 1954 R. 1. WARD RELAYING SYSTEM Filed April 26, 1952 6 Sheets-Sheet 4 /25 l lv 1l INVENTOR. 6/ fiabe/z* Z Ward,

Oct. 19, 1954 R. n. WARD RELAYING SYSTEM 6 Sheets-Sheet 6 Filed April 26, 1952 l 'Z a M wd, W w fw W 4 0. @/QM wf@ MWMS 57W q 1f Y @@m im J w ,keum go @Q l Y 7 B a@ Mw w V V V 0 L w W w mw@ 3 .h A 66 4 v J0 0 6 E -J ,f @fw n DMn 7 W m M .L W www M l? N m p a i m 5 14mm n2 f m 23 6 w T1 w w 6. e, w lH L ,M 1 w/ Patented Oct. 19, 1954 UNITED STATES OFFICE RELAYIN G SYSTEM" Robert I.' Ward, Itasca, Ill.` Application April'26,` 1952l`,SerialN. 284,551 4 Claims; (Cl. 317-28) My invention relates, generally, to relaying systems, and it has'particular relation tov dif-v ferential relaying systems for alternating current powertransmission lines inwhich the con trol from the opposite ends isv effectedr by carrier current The present invention coiistitutesian improvela over and a further development of the differential relaying systems disclosed in my prior atents 2,147,781 and 2,213,294, and in my copending application Serial No. 676,605, nled June 14, 1946, which has since issued on April 29, 1952, as: Patent 2,594,371. priorpatents I have shown how differential protection can'be provided for an alternating current electric power transmission line by employin'gelectrie valves,` one at each end of the line,

and by controlling the conductivity of theva'lve a't` each end by certain conditions at the other end of the line; In these two prior patents,v the connecting'link between the two ends of the line .for control purposes was provided by pilot conductors which provide a direct electrical interconnection'over metallic paths.

In'my'aforesaid copending applcatifl, Serial erably employs a phase angle comparison method of' control, which responds to particular line faults, such as internal tion' being-protected.-

Referring` now to the improved relaying systentidisclosed` inv2 the present application, I have retained the above carrier current embodiment of" phase angle comparison method of control for protecting'- the installation against line faults, but" have supplemented'the relaying system by a sir-called ;rai1'-fcr trib contrelf for protecting 'nstallationagainst power transformer faults. well. The desirability of line protection against power transformer faults can be illustratedv by referring nrst to the type of power transmission line installation disclosed in my copending application, wherein the oil circuit breakerwhich responds' tothe protective relaying 'scheme is located between the power trans-v formers and*the'line,` as a result of which the In the rst two mentioned;

line faults inthe sec-v Cil 2.. powertransformers do not need to be included inl` the linefrelayingscheme. However, in order to reduceithe cost of high line installations it is oftentimes desirable and sometimes the practice to omit the line side oil circuit breakers, so'l that in such typel of installation the lines are connected directly to the power transformers. Such installations present the problem of includingthepower transformer in the line relaying scheine'. The additional control to take care oftransfornir faults requires provision for not only tripping the local oil circuit breaker on the primary "side ofthe -faulted power transformer, but tripping the remote end of the line as well; This I accomplish by my improved transfer trip control', whichI-'superpose upon the carrier relaying scheme of' the phase angle comparison control;

This improved transfer'trip controlis based upon a unique differential frequency relation whichis41 initiated or set into operation upon theoccurrence of a transformer fault, and whichv differentialfrequency relation is then transmittedfto theremotek end of theline over the same carrier channel that transmits the phase angle comparison control. At the remote end of the line, this differential frequency relationthen acts upon a transfer trip relay for tripping the circuitbreaker at that end of theline so that both ends oftheline are opened upon the oc-V currenceof'the power transformer fault. The appara-tus employed for maintaining the continuously functioning phase angle comparison control embodies transmitters at opposite ends ofthe linehav-ing; continuously oscillating transmitter tubes. As a precautionary measure, each transmitter preferably employs two such tubes which oscillatev at the same or substantially the` same frequency; whereby if thereshould be a failure of one tube the phase angle comparison control willv still' be maintained effective by the other transmitter tube. I obtain the above transfer trip control by detuning one or both of these transmitter tubes from its normal oscillating freduency so as toestablish a differential frequency relation between the two tubes, this differential frequency relation then being transmitted to the other end of the line for causing operation of the transfer trip relay as above described. This detuning operation is made to occur immediately upon the occurrencey of the 'transformer fault, so that the dierential frequency relation is made operative to effect prompt tripping ofthe remote end of the line. The differential or beat fre- 55 qufency established between the two oscillating frequencies by the detuning operation may be of relatively small magnitude, such as in the range of an audio tone signal.

From the foregoing, it will be seen that it is one of the objects of the present invention to provide an improved relaying system in which a transfer trip control, which is responsive to power transformer faults, is superposed upon a carrier current type of phase angle comparison control which is responsive to line faults in the section. All of the operating advantages of the phase angle comparison control are retained in the new system. Furthermore, substantially the same apparatus used in the phase angle comparison control is used in the operation of the transfer trip control, so that very little additional cost is involved in the new system. Thus, my improved relaying system makes it practicable to omit the line side oil circuit breakers in a greater proportion of new installations.

Other objects, features and advantages of the invention will appear from the following detail description of one preferred embodiment thereof. In the accompanying drawings illustrating such embodiment:

Figure 1 illustrates schematically the important features of my invention;

Figure 2 illustrates, graphically, the phase relationship between the currents and voltages at opposite ends of the line and the pulses transmitted by the transmitters during through fault or normal load conditions;

Figure 3 illustrates, graphically, the relationship referred to in Figure 2 on the occurrence of an internal fault; and

Figures 4, 5, 6, and 7, placed side-by-side in the order mentioned, illustrate diagrammatically the circuit connections that may be used in practicing my invention.

Referring now particularly to Figure l of the drawings, it will be observed that the reference character I6 designates conductors of a three phase system which may be supplied from a suitable source of alternating current, such as a 60 cycle source. The conductors ID are arranged to be connected by a circuit breaker, indicated generally at Il and having a trip winding I2, to energize an alternating current polyphase transmission line comprising conductors I3. As indicated by the broken lines, the conductors I3 are of indefinite lengths, for example, they may extend over several miles and even into the hundreds of miles. The conductors I3 are arranged to be connected by a circuit breaker, shown generally at I4 and having a trip winding I5, to conductors I6. The conductors I6 may be connected to another source of power or they may be connected to various load circuits or they may be connected to a combination of power source and load circuits. It will oe observed that the ends of the alternating current transmission line comprising the conductors I3 are designated as A and B.

As above remarked, in my copending application Serial No. 676,605, I have disclosed a protective relaying system for the above type of power transmission line using a phase angle comparison mode of control effected from opposite ends of the line by carrier current transmission. In the type of power transmission line installation disclosed in that application, the oil circuit breaker which responds to the protective relaying scheme is interposed between the power transformers and the line, and hence the power transformers do not need to be included in the line relaying scheme. However, in order to reduce the cost of high line installations, it is sometimes the practice to omit the line side oil circuit breakers, so that in this type of installation the lines are connected directly to the power transformers In Figure l, I have schematically indicated this type of installation, with the power transformer 260 interposed between the oil circuit breaker II and the line conductors I3. Such installations present the problem of including the power transformer in the line relaying scheme. As previously described, my invention employs a carrier current type of phase angle comparison relaying system for protecting the installation against line faults. In order to protect the installation against power transformer faults as well, I superpose an additional control upon the carrier relaying scheme of the phase angle comparison control, which additional control I term a transfer trip control. This additional control requires provision for not only tripping the local oil circuit II upon a fault occurring in the power transformer 20D, but tripping the remote end of the line as well, such as at the oil circuit breaker I4. In the following description, I shall first describe all of the apparatus functioning in the phase angle comparison relaying system for protecting the installation against line faults, and shall then describe the apparatus functioning in the transfer trip scheme for protecting the installation against power transformer faults. Cross reference is also made to my aforesaid copending application in connection with the phase angle comparison relaying system for protection against line faults.

Referring now to such latter relaying system, in the event there is an internal fault on the alternating current transmission line comprising the conductors I3, such as a short circuit between two of the conductors as indicated at X, it is desired that both circuit breakers II and I4 at the ends A and B of the line be opened by operation of their respective trip windings I2 and I5. This is to prevent power being fed from the conductors I0 to the fault and likewise to prevent power being fed thereto from the conductors I6 in the event that they are connected to a power source.

It is required that means be provided for distinguishing between an internal fault, such as the short circuit at X, and a through fault which is a fault that occurs outside of the alternating current transmission line comprising the conductors I3, for example, a short circuit occurring between two conductors I6. For present purposes it is desired that the relaying system be able to distinguish between through fault conditions or normal load conditions on the one hand and internal fault conditions on the other hand for the purpose of selectively operating the circuit breakers I I and I4.

In accordance with my invention, I employ the variable conducting characteristics of a thermionic valve which comprises essentially a hot cathode, a plate and a control grid. When an alternating potential is applied to the plate and to the control grid, the valve remains in the non-conducting state when the voltage applied to the plate is out of phase with the grid voltage, it being assumed of course that the magnitude of the voltages applied to the grid and plate are sufficient to maintain the valve in the non-conducting state. Now when this phase relationship is altered so that the voltages ap- .plied to the-grid andplatefaresubstantially'in phase and are of sufficient magnitude, ythe valve Ywill `become conductingiand current will flow in the plate circuit.

VProvision is made, in accordance-with my invention, to obtain a voltage at each of the-ends vA and Bof the alternating current transmission .line comprising conductors ls, which corresponds in magnitude and lphase to the current flowing in ythe transmission line and 'the direction of .power iiow therein. This derivedvoltage or potential is employed for two purposes. One of these purposes is tocontrel the potential. applied to vthe plate of the thermionic valve associated with the corresponding end of the line. The other is to control the operation of ya carrier transmitter whose output is applied in conventional man ner to thetransmission line'for reception at the opposite end. The means for derivingthe control potentials at the ends of the line are soconnected that, during through fault or normal load conditions, the control potential at one end of the line is 180 out of phase with that at the other end.

At each end of the line there is provideda receiver and associated therewith is a rectifier ywhich may be considered to be a part of the receiver. The receiver is arranged to receive, not only the output from the distant transmitter but also theoutput from-the local transmitter, I

assuming the two transmitters to be operating on substantially the same frequency. The receiver may comprise a radio frequency amplifier and detector or rectifier. .The transmitters may transmit on the same frequency. The transy mitters are controlled by the derived control potential at each end so that they transmit during successive half cycles of the frequency of the alternating current applied to the line during through fault or-normal load conditions. impulse received at one end of the line fromthe distant station is rectified as a negative impulse or blocking pulse, and it is vapplied to `the control grid of the thermionic-valveduringthe half cycle that the control potential applies a postive potential to its plate. vAs a result the valve remains non-conducting and the relay winding in the plate circuit, connected-to energize the trip winding I 2 or l5 of thecircuit breaker l I or M, is not energized.

Now, on the occurrence of an internal fault, such as the short circuit as indicated'at X, the derived potentialat one end of the alternating current transmission line visshifted in phase.

For example, it may be shifted 180\ or more in l phase, vdepending upon the constants of the circuit at the time that the'fault occurs. As a result of this phase shift the transmitted blocking signals are shifted so that they do not block conduction in the phase angle comparison tubes 3'1--3'1 and 38-38 at opposite ends of theline. Hence, these phase angle comparison tubes3l- 3l' and 3-i`8 now become conducting, 'energizing the relays :i5-l5 which trip the line'oil circuit breakers ll andii-atopposite ends ofthe line. This removes the faultedtransmission line from the power system.

As illustrated diagrammatically in Figure i of the drawing, the out-of-pliase`l control potentials may be obtained by current transformers having secondary windings 2l and 22 at the ends A.aand B, respectively, of the transmission line comprising the conductors I3. The secondary windings r.2i and 22 are'connectedinductively and conductively with secondary windings of .transformers 123,

The ,fl

23a land 124, 24arrespective1y, and with windings 25 and 26 which constitute the primarywindings voftransformersl .an`d328, the cores of which are arranged-to saturate `on predetermined iiow of current lthrough the windings 25 and r26 so as to limit the voltage that is generated in secondary windings 29 and, 3l and 32 on the transformers A2'! and 28, respectively. The. purpose of thesat- 4urating transformers 21-28 is to protect the transmitters vtil-'34 and the phase angle comparison tubes 37-31 and 38-38 from the excessive voltages during external fault condition. The phase angle comparison tubes 31-38 do not conduct onthrough fault because of the blocking signals from the opposite ends of the line. Duringl this half of the cycle the saturating transformer.25or V26 isunloaded, Which might permit its secondary voltage to exceed safe limits for its` associated equipment. To limit this voltage, the iron ofthe transformer is saturated on overload conditions. If itis desired to further protect the equipment, spark gaps g and g may be provided across either or both secondaries to limit the peak voltage. The auxiliary current transformers 23-23a and 2li-2da have different ratios so as to provide a single phase component of current from a three phase system. For example, the auxiliary transformers 23a and 24a may each have a ratio of 2 to 1, and the auxiliary transformers 23 and 24 may each have a ratio of 4 to 1. The polaritiesof these current transformers are so connected that their secondary currents add vectorially in the primaries of the saturating transformers '2l and 28. This current is 43% of the secondary current of the line current transformers when theabove phase currents are balanced. In Le Clair et al. Patent No. 1,919,231, and also in my prior Patent 2,023,653 (page 4, column 2, lines 26-2'7) there is set forth an explanation of the functioning of the windings 2l through 26, just referred to, and, accordingly, a more complete description of the manner in which the connections are made and the phase relationships of the current flowing therein will not be set forth. It will be understood also that suitable networks, such as sequence lters, can be usedto supply current for saturating transformers 2l and f8.

The ends A and' B of the transmission line have yassociated therewith transmitters 33 and IMI. In general, the transmitters 33 and 34 are of conventional construction and both are arranged to transmit at the same frequency which, 'for lcarrier current purposes, is in the range from approximately 50 to `3G() kilocycles. Receivers and rectiners' and it are associated with each end of the transmission line Aand they are arranged to receive and rectify impulses received from the opposite or distant end of the line or transmitters `33 andtll.

The phase angle comparison tubes or valves are indicated., generally, at 3l and 3'8 for each end of the line. `In general, each of the valves 31 and @s comprises, respectively, a plate tik-lid, a control andai- 42, and a hot cathode f3-IM. As will appear hereinafter, a multigrid tube is used, but, forpurposes of simplication, the additional `grids are not shown in Figure l. Control relays, indicated generally at :d5 and 45, have operation windings di' and di? connected to the plates 39 and tlrespectively. They have normally open contacts is and "5t which are arranged to energiae trip windings i2 and i5.

.For purposes of illustration, it will be assumed that power"l flows in the transmission line comprising conductors I3 from A to B, as indicated by the arrows I. Further, it will be assumed that through fault or normal load conditions exist. Under these assumed conditions, during the half cycle of the 60 cycle alternating current that is being applied by the secondary winding 3| to control the transmitter 33, it may be assumed further that this half cycle is positive. During this half cycle the transmitter 33 applies an impulse to one of the conductors I3 through a variable capacitor 53.

During this half cycle the conditions are such that the secondary winding 29 applies negative potential to the plate 39 of the valve 31.

At the other end of the line, during the half cycle just referred to, while the transmitter 33 is transmitting, the secondary winding 32 of the transformer 23 applies negative potential to the transmitter 34 and, consequently, it does not transmit. During this same half cycle the secondary winding 33 applies a positive potential to the plate 48 of the valve 38. However, since the impulse transmitted from the transmitter 33 is received and rectified by the receiver and rectifier 36 and is applied to the control grid 42 in the form of a negative pulse, the valve 38 is effectively blocked from conducting. During the next half cycle when the transmitter 33 is not transmitting and the transmitter 34 is transmitting, the polarities previously referred to are reversed. The valve 31 is prevented from becoming conducting by the negative pulse applied to its control grid 4I which originates in the transmitter 34. Accordingly, the valve 3'I is maintained in the non-conducting state. Since negative potential is applied to the plate 40 during this particular half cycle, the valve 38 is rendered nonconducting. It will be noted that the transmitter 34 applies its output to one of the conductors i3 through a variable capacitor 54.

In Figures 4, 5, B and 7 of the drawings the circuit connections, illustrated schemactically in Figure l, are shown in detail. It will be noted that the contacts 49 and 53 of the control relays 45 and 46 are connected in series with paralleled contacts 55 and 56, respectively, of fault detecting relays, indicated, generally, at 51 and '58 which have operating windings 59 and 60. The operating windings 5S and 6D are connected, as shown, in series circuit relation with the secondary windings 2l and 22, so that on the occurrence of predetermined fault conditions operation of the relays 5S and 63 is effected. It will be noted that, on operation of the relays 45 and 4S, the respective trip windings I2 and I5 are not energized unless one of the relays 51 or 58 is also operated to complete the energizing circuit. If desired, the fault detecting relays 51 and 53 may be used to start and stop the transmitters 33 and 34 so that intermittent rather than continuous operation thereof is aorded.

Any suitable source of control voltage can be used, not only for energizing the trip windings I2 and I5, but also for applying the necessary control potentials for the various thermionic valves that are used. As illustrated, at end A conductors 6I, 6i' represent the conductors of a 240 volt direct current bus. Likewise, at end B conductors 62, 62' represent a similar bus.

Each of the phase angle comparison tubes or valves 31 and 38 has a duplicate valve connected in parallel circuit relation therewith. The reason for this is to prevent any impairment in the operation of the system should one of the valves 31 or 38 fail for any reason. It will be noted that each of the valves 3I and 38 is provided, respectively, with a suppressor or grid 63--64 and a screen grid B5-66.

The transmitters 33 and 34 include electric valves 61-68 and (S9-10, respectively, which are connected in push-pull or parallel relation. Two valves are provided for each transmitter, so that in the event that one of them fails the operation of the system will not be impaired. In the adaptation of my improved trip control to the phase angle comparison control which I have been describing thus far, I utilize the two tubes 61 and G9 of transmitter 33 to generate the transfer trip signal, such being an audio frequency tone signal, as I shall later describe. Each of the valves 61-68 and 69-13 comprises, respectively, a plate 'I I 12, a screen grid 13-14, a control grid 15-16, and a hot cathode 11--18. The plates 1I and 12 are connected to the ends of a primary winding 13-80 of transformers 8I-82, having secondary windings 233-84. As shown, the secondary windings 83--34 are connected through variable capacitors 85-36 to inductors 31-88 which are connected to the variable capacitors 53-54, previously referred to. Variable capacitors 89-90 are provided for the purpose of tuning the plate circuits of the valves 61-68 and BSI-10.

During the operation of the phase angle comparison control, the frequency of the transmitters 33 and 34 is controlled by oscillating circuits 9I-92 which comprise, respectively, inductors 93-94 and variable capacitors Sli- 96. The control potential is applied to the control grids 15-1B through resistors 91-98 from secondary windings 3I-32 of the saturating transformers 21-28. The necessary biasing voltages for the transmitters 33 and 34' are provided from the sources 6I and E2 through resistors SSI-|00 and variable resistors IOI-I2.

Each of the receivers comprises electric valves ID3- |04 and IOS-IUE. They are connected in conventional manner to form dual radio frequency stages. In the event of failure of one of the valves in each receiver then the system will continue to function using the other valve alone. The valves ID3- |04 and IUS- |05 comprise, respectively, plates I01-I08, suppressor grids IUS-I I0, screen grids III-I I2, control grids II3-II4 and hot cathodes II5II6. The incoming signals are applied to the control grids |I3 and II4 from secondary windings II1--II8 of transformers IIS- |20 which have primary windings I2I-I22 that are connected through variable capacitors I23-i24 to the variable inductors 81-88. Variable capacitors IIT-IIB serve to tune the circuits to the control grids [I3-I I4 to the desired frequency of the transmitters 33-34.

The outputs of the valves IUS-|05 and |04- |08 are applied to primary windings I 25-I26, respectively, of transformers l21-I28 which have center tapped secondary windings IZB-|30. The secondary windings IZB- |33 are connected to rectier valves ISI-|32 and I33-I34 which comprise the rectifier previously referred to. The rectifier valves IBI- 32 and ISS-|34 comprise, respectively, plates |35-I35 and hot cathodes I31-I38. The outputs of the rectifier tubes I3I-I33 and I32--l34 are applied across resistors I39-I40 and thereby through resistors I4 |42 to control grids 4I-42 of electric valves 31-38.

In Figure 2 of the drawings the operation of the differential relaying system using carrier current as sine waves.

tro-l grids 42 of the valves 38.

with each other.

Curves M-MG represent the voltages that are applied by the secondary windings 3 i-SZ, respectively, to the control -grids i5-lf3 of the transmitter valves 61-69 andt8-l0- For illustrative purposes the curves [e5-litt are shown However, the wave form |will be distorted under fault conditions resulting from saturation of the cores of transformers A2l and 28. It will be noted that these waves ldd-M6 also are 180 out of phase with each other under the conditions assumed. Since the transmitters 33-3 can transmit only when their control grids are positive, during the first half cycle oi the alternating current here under consideration, the transmitter 33 is transmitting while the transmitter 34 is not. This results in apulse i471 being applied by the transmitter 33 to its receiver and rectier 35 and a similar pulse Hi8 being applied to the distant receiver and rectifier 36. During the next half cycle the transmitter 33 does not function while the transmittertd transmits. It transmits a pulse 49 to the opposite end of the line and a local pulse It whichis received by its receiver and rectifier 36. It will be understood that the pulses itli138 in reality constitute a single pulse and that each is made up of a number of waves of the carrier frequency. They are shown separately for illustrative purposes. The same comment applies to the pulses ille-|50 from the transmitter 34. The pulses Ille-lds are rectied by the rectier tubes ESE- |33 and R32-i311 respectively. The rectier blocking pulses are indicated at l5! and |52 for each end of the'line.

Now it will be observed that, during the half cycle that the transmitter 33 is transmitting, a rectied blocking pulse 152 is applied to the con- During this half cycle, as illustrated in Figure 1, the plates 40 of these valves are positive. However, because of the negative blocking pulse |52 being applied thereto during this half cycle, the valves 38 are rendered non-conducting. Also, during this half cycle, since the plates 39 of the valves 3l are negative, they are not rendered conductive. Likewise, during the next half cycle, when the plates 39 of the valves 37 arepositive, the rectifier blocking pulse l5! is applied to the control grids dl and the valves 31 are effectively blocked from conducting current. During this half cycle the plates 40 of the valves 33 are negative, so that these valves are maintained in the lno-nconducting state.

Thus, it will be apparent that as long asthrough fault or normal load conditions exist, the valves 31 and 38 will be maintained in the non-conducting state and windings lll-48 of the relays fi5- 43 will not be energized. This is due to the fact that a negative blocking pulse is applied to the valves 31-38 from Vthe opposite end of the line during each of the half cycles that the plates 39-40 thereof are positive.

Now reference may be had to Figure 3 of the drawings to indicate what takes place on the 10 occurrence or internal fault conditions It-will be assumed that the power flow is in the direcltion indicated by the arrow 5l in Figure l, and that the internal faultis represented by a short circuit between the conductors i3, as indicated at X; or alternatively by a short between one of the conductorsrand ground, as indicated at Y, in which case current would i'iow from opposite ends of the line to the ground fault, as represented'by the arrows 15a and i512. Under these `assumed conditions the sine waves HSE-Md, in-

stead. of being out of phase with each other, as indicated in Figure 2, `are brought into phase with each other, as indicated in Figure 3. Likewise,-the lvoltages represented by the sine waves M5-itt applied to the'transmitters 33-34 are in phase with eachother. The transmitter 34 transmits during the same half cycle that the `transmitter 33 transmits, so that both transmitters are transmitting in the half cycle that -the plates 39 'and di) of the valves 3i and 38 are negative. During the neX-t half cycle when the plates 3Q-dii are positive,` no impulse is transmitted vby either transmitter 33 or v31A. Consequently, the valves fil-til are unblocked and current hows intheir plate circuits, as indicated 'bythe waves IES-i521'. in Figure 3. The windings "lll-133 of the relays i5-lit are energized and contacts iS-5@ thereof are closed. Assuming further that theiault is of such character that -one of each or" the relays 5l anda is energized,

the circuits for energizing the trip windings `I2 and i5 will be completed through contacts 55 yand-tit. The circuit breakers l l and Iii are tripped and the line is disconnected at each end from the system.

It is desirable that there be an indication of :the strength oi the signal that is being received from the opposite end of the line. That is, it is desirable that indicatingimeans be provided at the end A for indicating the strength of the signal that is being received from the transmitter 34 atend B` and vice versa. When the'system is arranged to'transmit the carrier frequency from each end continuously, a continuous indication control grids IBL-I Si! and hot cathodes ite-lll).

The meters E525-15E are connected in the plate circuits of the valves lSl-lt2 and across their respective direct current busses 6i-t2 through lresistors l'i I-ll2, and through variable resistors H13- Vid Companion variable resistors 173'- llld are also connected between the negative direct current busses 6I', 62 and the cathodes i3-M and suppressor grids 63--64 of the tubes Blk-38.

With neither of the transmitters 33 or -34 transmitting, the voltage applied tothe plate circuits of the valves itl-|62 is adjusted so that the pointers itl-e158 have substantially a full scale deection. Now during the half cycle that the local transmitter is transmitting, the valves itl-m2 are blocked so that they are non-conducting. This is due to the relatively high negative bias appliedto their screen grids i65-i66. During the next half cycle the screen grids |65- |66 are positive, vand hence render the valves [6l- FB2 conducting. The degree that the valves BBL- |62 are rendered conducting depends upon the magnitude of the rectified negative blocking pulse which is applied across the resistors i3d-|00 by the transmitters at the opposite ends of the line. Consequently, during this half cycle the pointers |51--l 58 are deiiected less than full scale. The meters |55|56 can be calibrated so that there will be zero deection when the strength of the received signal is at a maximum. Therefore, the position of the pointers |51-I58 between their zero positions and full scale deflections will be indicative of the strength of the individually received signal from the opposite end of the line.

It will be understood that the differential relay system using carrier current control disclosed herein may be defined as a pulse modulation system. However, it will be understood that frequency modulation or amplitude modulation can be employed instead of pulse modulation.

The foregoing concludes the description of the phase angle comparison relaying arrangement for protecting the system against line faults. I shall now describe the transfer trip arrangement for protecting the system against faults arising in the power transformer 200. Faults arising in this transformer 200 are arranged to cause operation of a transformer differential relay 20| of conventional or any desired design. This relay comprises a cooperative relation of differential coils 204-205 so arranged that a fault in the power transformer 200 energizes the operating coil 204 of the relay. The current in this operating coil 204 is the difference between the currents from the current transformers 206 and 201. Under normal conditions, these currents are balanced or equal. If power is consumed by a fault in the power transformer 200, these currents become unbalanced, and the unbalance current iiows in the operating coil 204 of the relay 20|. The fault current may be large enough to actuate the differential relay 20|, and yet not be of sufcient magnitude to operate the regular line relaying arrangement utilizing the phase angle method of control previously described. For example, the differential relay 20| responsive to power transformer 200 is usually much more sensitive than the line relays. Accordingly, some form of signal transmission must be available to communicate to the opposite end of the line the fact that the differential relay 20| has operated, in order that the line may be deenergized. The amount of damage that will ensue to the power transformer 200 upon the occurrence of a fault therein will depend upon the length of time that the transformer remains energized after being faulted.

The operation of the differential relay 20| closes two sets of normally open relay contacts 20m and 201D, the contacts 20|a energizing the tripping coil l2 of the oil circuit breaker for instantly opening the line at the local end, and the other relay contacts 2 |0b energizing the winding of the transfer trip auxiliary relay 2 |0. This auxiliary relay comprises four sets of normally open relay contacts 2|0a, 2|0b, 2|0c and 2|0d which move to closed positions upon the energization of this auxiliary relay. The contacts 2|0a and 2l0b place a more positive bias on the control grids -15 of the two transmitter tubes (i1-69, this more positive bias being taken from the adjustable tap on the voltage divider |13 through conductor 2|2, resistor 2|4, relay contacts 2|0a. and 2|0b and conductors 2|6 to the control grids 15--15, thereby taking the control 12 away from the phase comparison circuit and pro viding continuous oscillation of the transmitter tubes. The closing of the third set of relay contacts 2|0c introduces the variable capacitor 2|1 in shunt across the variable capacitor in the tuned control grid circuit of oscillator tube 69; and the closing of the fourth set of relay contacts 2|0d introduces the variable capacitor 2I8 in shunt across the variable capacitor 89 which is in the tuned plate circuit of oscillator tube 69. Prior to the operation of the transfer trip auxiliary relay 2|0 and the closing of the relay contacts 2|0c and 2|0d, the two oscillator tubes 61 and 69 oscillate at the same frequency, as disclosed in my copending application. The tank coils and tuned circuits of the transmitter are loosely coupled so that the failure of one circuit or tube will not detune or retune the remaining oscillator, only sufficient coupling being required to keep the two oscillators in synchronism. During this phase angle comparison operation of the system, both oscillators are operated at the same frequency. Since these oscillators are loosely coupled, they may be operated at different frequencies, provided the circuit constants differ sufficiently to over-ride the effect of the loose coupling. The transfer trip operation, brought about by the energization of the relay 2 l0 and the closing of the contacts 2 |00 and 2 |0d, causes the two oscillators to operate at different frequencies. In this transfer trip operation, the oscillator 69 is slightly detuned from its normal channel frequency by the introduction of the above capacitors into the tuned circuits. For example, if the normal channel frequency is kc., the oscillator B1 will be tuned to this frequency (fl) and will continue to operate at this frequency, but the other oscillator 69, by reason of the detuning operation, will operate at some other frequency (f2) which may be above or below fl. For example, this frequency f2 may be 10l kc. The difference, f2-f|, or l kc. will be eiective at the remote end receiver as an audio tone of l kc. This suggested frequency difference of approximately 1 kc. is merely illustrative, because the introduction of the capacitors 2|1 and 2|8 into the tuned circuits can be made to change the frequency of these circuits to any desired degree, depending upon the circuits and capacitors used, etc. For example, if crystal control is used to control the oscillators 61 and 69, the difference between the normal or original frequency fl of the oscillator 61 and the changed frequency f2 of the oscillator 69 may be reduced appreciably. These two frequencies fl and f2 are transmitted simultaneously over the line to the remote terminal thereof. At that end of the line, the receiver 36 receives the dual signal. This dual signal is rectified at the receiver detector consisting of the two rectiers |32| 34 connected back to back. The beat signal f2--fl is applied through the filter 222 which is pretuned to this frequency (fl-f2) or (f2-fl). This lter 222 is a high Q filter which permits high attenuation of all except the proper signal. From this filter the signal is conducted through conductors 226, 221 to the amplifier tube 228 of transfer trip relay network 229, where it is amplied and then again further filtered in lter 230 to prevent unwanted signals passing to the relay tube 232. This latter lter 230 is also provided with a time delay circuit to prevent operation on noise due to switch arcs, etc. This filter 230 can be made more effective by using a crystal frequency control if necessary. The signal from the filter 230 i's 'used 'to'plac'e a lpositive bias "on the relay tube 1232, 'which operates the plate circuit relay 234. The 'contacts 236 of this krelay 23B energize the trip winding l and trip the oil circuit breaker i4. The components and connection of thetransfer trip relay network 229 will be well understood by those skilled in the art from the illustrati'on thereof in Figure 7,

vInlorder to'have the system operate with maximum effectiveness and reliability, particularly to have the transfer trip respond immediately to faults in the power transformer 2te, it is desirable that the receivers 35 and 3S at both ends `of the line remain energized at all times. The transmitters 33 and 34 may normally stand idle, or they may be operating at all times in the performance of the phase angle comparison control. 'I lwish 'it'to be understood that one end of the fline might operate at one frequency and the 'other end of the line at another frequency. Also, 1transistors may be used in place of heated cathode tubes, wherever applicable. My improved system enables a transfer trip signal to be transmitted over a carrier relaying scheme with minimum complexity and cost of equipment, and with the greatest reliability. Heretofore, existing systems have used tone modulation to transmit an audio tone to a tone receiver at the remote end of the line. This requires the addition vof 'modulating equipment which in turn reduces the reliability of the relaying equipment. -In the present invention, I have modified or reconstructed the carrier relaying scheme of my prior application Serial No. 676,605 to provide a `transfer trip signal to be transmitted to the Vremote end ofthe line without the addition of `modulating equipment, or without very extensive Amodification of the carrier relaying scheme. This application is a lcontinuation-impart of my coipendingapplication Serial No. 676,605.

While I have illustrated and described what I-regard tobe the preferred embodiment offmy invention, nevertheless it will be understoodthat such is merely exemplary and that numerous modifications and rearrangements may be made 'therein without departing from the scope of the invention.

I claim: Y

l. In a protective relaying system for an alternating current polyphase transmission line `having a circuit breaker at each end, a power transformer at one end located between the adjacent circuit breaker and the line, and tripping mea-ns for tripping said circuit breakers, the combination of a phase angle comparison type of protecting apparatus at each end of the line comprising phase angle comparison tubes, carrier `current transmitters and receivers at oprposite ends of the line for establishing carrier ycommunication over said line between said phase angle comparison tubes, each of said carrier current transmitters comprising two oscillator tubes, means responsive to an internal fault condition on the line for changing the phase angle relation in said phase angle comparison tubes, means responsive to said changed phase angle relation for operating said tripping means to trip said circuit breakers at both ends of the line, said two oscillaltor tubes normally oscillating at substantially the same frequency during all normal load conditions and internal-fault conditions on the line, transfer trip means comprising relay means responsive to a fault condition in said power transformer for tripping the circuit breaker at that end of the line and for also causin'gthe two oscillator tubes inthe adj acent trans- -mitter 'to Aoscillate at two different frequencies andtotransmit these two frequenciesto the-remote end of the line, and means at the remote end of the line responsive to the beat .frequency produced between said two diiferentfrequencies for tripping the circuit breaker-at that end kof the-line.

2. In a 'protective relaying system foran 'alternating current polyphase transmission line having a circuit breaker at each end, tripping means for tripping said circuit breaker, and -a power transformer at one end ofthe line'located -between the-associated circuit breaker andthe line, the combination of protecting apparatusat each end ofthe line comprising a relay tube conlload conditionscn said line, potential deriving vmeans operatively connected with the line vfor supplyingphase angle comparison vrpotentials/'to the plate circuit of said relay tube andto said carrier-current transmitter, said carrier-current transmitter comprising two transmitting tubes each having a control grid connected with said potential deriving means, and having a plate circuit coupled in carrier transmitting relation with one of the conductors of said transmission line for transmitting carrier pulses over said'lin'e,

`said two transmitting tubes normally oscillating at substantially the same frequency during I'all normal load conditions and all through-fault and internal-fault conditions on the transmission line, said carrier-current receiver comprising ka receiving tube having a control grid operatively -connected to receive the carrier pulses which are carrier transmitted from the other end of the line, and having a plate circuit operatively 'connected with the grid circuit of said relay tube, said carrier-current transmitters transmitting carrier pulses over said line from opposite endsl ythereof continuously in alternate half 'cycles throughout all normal load conditions and through-fault conditions, and transniittingsaid carrier pulses in the same half cycle during internal fault conditions on the line, and transfer trip apparatus comprising relay means vresponsive to a fault condition in said power transformer for tripping the adjacent circuit breaker and for causing the two transmitting tubes in the adjacent transmitter to operate at two different frequencies and to transmit these two different frequencies over the carrier channel to the remote end of the line, and means at the remote end of the vline responsive to the beat frequency produced between said two different frequencies for tripping the circuit breaker at the remote end of the line.

3. In a protective relaying system for an alternating current transmission line having a circuit breaker at each end, tripping means for tripping said circuit breaker, and a power transformer at one end of the line located between the adjacent circuit breaker and the line, the combination therewith of protecting apparatus at each end of the line comprising an alternating current phase angle comparison tube comprising plate and grid circuits, a carrier-current transmitter operatively connected with the line for transmitting a modulated carrier frequency in the form of carrier pulses to the control grid circuit of the phase angle comparison tube at the other end of the line, a carrier-current receiver operatively connected with the line for receiving the carrier pulses from the far end of the line and including means for applying such pulses as negative pulses to the grid circuit of the associated phase angle comparison tube, potential deriving means operatively connected with the line for supplying first and second alternating current phase angle comparison potentials, means for feeding one of said alternating current comparison potentials to the plate circuit of said phase angle comparison tube, means for feeding the other of said alternating current comparison potentials to said carriercurrent transmitter for modulating the carrier frequency to produce the aforesaid carrier pulses for transmission to the other end of the line, said phase angle comparison tube being normally conductive when the positive half cycles of said alternating current comparison potential are impressed upon said plate circuit unless said carrier pulses from the other end of the line are impressed on said grid circuit in time phase with said positive half-cycles to function as negative blocking pulses, means responsive to internal fault conditions on the line for shifting the time phase of said carrier pulses so that they cannot function as blocking pulses with respect to said positive half-cycles, whereby plate current flow occurs through said phase angle comparison tube under internal fault conditions, means thereupon responsive to plate current flow through said comparison tube for causing operation of said tripping means, said carrier-current transmitter which is disposed adjacent to that end of the line having the power transformer interposed between the circuit breaker and the line comprising two oscillator tubes and cooperating tuned circuits controlling the oscillatory frequency of said latter tubes, said cooperating tuned circuits being adjusted to cause the two oscillator tubes of said transmitter to oscillate together at substantially the same frequency while the relaying system is operating normally under no-fault conditions, and transfer trip apparatus for protecting said power transformer comprising relay means responsive to a fault condition in said power transformer for tripping the circuit breaker at the adjacent end of the line, detuning apparatus responsive to said latter relay means for detuning one of said tuned circuits whereby to cause said two oscillator tubes to oscillate at two different frequencies and to transmit such two frequencies over the-carrier channel to the remote end of the line, filter means at the remote end of the line for separating such two different frequencies from the phase angle comparison pulses, and means at the latter end of the line responsive to the beat frequency produced between said two different frequencies for tripping the circuit breaker at this end of the line.

4. In a protective relaying system for an alternating current transmission line for having a circuit breaker at each end, tripping means for tripping said circuit breaker, and a power transformer at one end of the line interposed between the adjacent circuit breaker and the line, the combination of protecting apparatus at each end of the line comprising a phase angle comparison tube having plate and grid circuits, potential deriving means operatively connected with the line for supplying an alternating current plate potential to said plate circuit at line frequency, a carrier-current transmitter for transmitting a carrier frequency over the line to the companion protecting apparatus at the other end of the line, said carrier-current transmitter comprising two tubes normally oscillating at the same frequency, means for modulating said carrier frequency to produce carrier pulses therein having line frequency, a carrier-current receiver for receiving said carrier pulses from the other end of the line and applying such pulses as control pulses to the grid circuit of the associated phase angle comparison tube, means responsive to said tube for controlling said tripping means, means responsive selectively to Athrough-faults and internal faults in the line for controlling the phase relation between the alternating current potential applied to said plate circuit and the carrier pulses applied to said grid circuit for controlling the conductivity of said phase angle comparison tube, whereby to cause operation of said tripping means in the event of an internal fault in the line, and also to cause operation of said tripping means automatically in the event of failure of carrier-current transmission independently of line fault, and transfer trip apparatus comprising means responsive to a fault condition in said power transformer for causing said two carrier-current transmitter tubes to operate at two different frequencies and transmit these two different frequencies over the carrier channel to the remote end of the line, and means at the remote end of the line responsive to said two different frequencies for tripping the circuit breaker at this end of the line.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,199,168 Cramer Apr. 30, 1940 2,393,717 Speaker Jan. 29, 1946 

